DE3417670A1 - PROGRAMMABLE FILTER - Google Patents

Description

6.J.P.Barnes - M.S.Hurley - A.R.BaxandaLL 18-4-1

Programmable fitter The invention relates to a programmable filter.

Programmable filters are used, for example, in order to receive signals with a given spectrum that are required for checking telephone systems.

The invention is based on the object of specifying a programmable filter whose frequency response is automatic can be adjusted.

The problem is solved by a filter according to the teaching of the main claim. The dependent claim contains an advantageous one Embodiment of the invention.

In the following, the invention is illustrated by means of an exemplary embodiment with the aid of the accompanying drawing further explained. The drawing shows a schematic Block diagram of a programmable according to the invention Filters.

The filter essentially contains a number of parallel-connected; Band passes, with a range of

ZT / PI-Bs / Bl

May 10, 1984 -4-

G.J.P.Barnes 18-4-1

a third octave each, isolation amplifiers at the and output and a control unit. The individual components of the filter are described below.

The filter has a modular structure. It contains an input / output module 1,. a number of filter modules 2 and a Control module 3. The modules are interconnected by a Address bus 41, a data bus 42, a control bus 43, an analog signal distributor 44 and an analog signal bus 45 connected. There are connections to the outside from the input / output module 1 via an analog input line 51 and an analog output line 52, as well as from the control module 3 via a connecting bus 53.

The input / output module 1 contains an input isolating amplifier 11, a gain adjuster 12, an over-control detector 13, an output amplifier 14, a Address decoder 15 and a data memory 16.

The input isolation amplifier 11 has a very low Self-noise on C 3 η V / iTT? at 1 kHz). Using the address decoder 15 and the data memory 16 can be the gain adjuster 12 and thus the gain of the input isolating amplifier 11 can be changed under program control so that the existing signal / noise ratio of the entire Filters can be used in the best possible way. The input isolation amplifier 11 also has a low resistance output to which the inputs of the filter modules 2 via the analog signal distributor 44 are connected.

The override detector 13 monitors the output of the Input isolation amplifier 11 and gives to the control module 3 a message if an overload occurs.

ft · η

G.J.P.Barnes 18-4-1

The output amplifier 14 sums the output signals of all channels provided in the filter modules 2 and produces a low-resistance output via the analog output line 52.

Each filter module 2 contains three independent bandpass filters 21, in the drawing with filter 1, filter and filter 3 are designated. Each bandpass filter 21 is preceded by a programmable attenuator 22 and an isolating amplifier 23 downstream. The attenuation of each attenuator 22 can be set in the range between 0 and 88 dB; it can also be set to infinity. The addressing and setting of the attenuators 22 takes place per filter module 2 via an address decoder 24 and a data memory 25. The addressing of the individual Filter module 2 C the address of the respective filter module 2 is set by a dual I-in-line switch designed so that all three bandpass filters 21 of a filter module 2 are set and used independently of one another can be or can be combined to form an octave filter. All data are cached, so that each channel is completely independent of the other; unless they are addressed as an octave filter.

The control module 3 processes all Protoko 11 signa Ie, the Data exchange etc., takes over the separation between address and data for the connected modules and generates the necessary control signals, for example a data transfer signal I, etc. The control module 3 requests Help is also available if the input / output module I 1 is overloaded is reported.

■ "ο ■ *

G.J.P.Barnes 18-4-1

The control module 3 contains dual-in-line switches with which both, the addresses of the connected filters are set as well as an operating mode can be selected. The selection of the operating mode allows a switchover between fast and slow operation, between "just hear" and "speak and hear" etc. (the normal operating mode is speaking and listening at high speed).

Each individual bandpass filter 21 (with a third octave) can be individually addressed by a 6-bit code as follows will. The two least significant bits select the single bandpass filter 21 or combine all three in one Filter module 2 contained bandpass filters 21 to an octave filter. The respective filter module is set with the remaining four bits 2 selected. Its address is with dual-in-line switches adjustable. See the table below:

(MSB) A5__A4 "A4__A2 Al AO (LSB)

Module address Bandpass address

A1 AO

0 0 lower third of the octave

middle third of the octave upper third of the octave whole octave

To set a bandpass filter, two (6-digit) Bytes are sent. The first byte is used to address the filter module and bandpass filter; with the second byte becomes the required attenuation is set. The weakening can be specified in steps of 0.375 dB.

-7-

0 0 0 1 1 0 1 1

- "7 -

G.J.P.Barnes 18-4-1

If, for example, in filter module 2 with the address 0100 (4-iq) the middle third octave is set to 12 dB attenuation, then the two consecutive bytes 17 _1Q and 32. «are to be sent as follows:

1. 17 ₁₀ = 0100/01 = filter module 4 / middle octave third 2. 32 ₁₀ = 32 χ 0.375 dB = 12 dB

If several bandpasses are to be set at the same time, these two bytes must be sent alternately, i.e .: bandpass, attenuation, bandpass, attenuation, ...

If a filter module 2 is to work as an octave filter (bandpass address is the same as 3.q), then all bandpasses 21 become this Filter module 2 set to the same attenuation and all previous settings are canceled.

The data transmitted in this way must not be terminated by a carriage return or line feed or the like will.

The setting of the gain of the input isolating amplifier 11 is similar. The module address 0 is used and the following data byte provides the gain in multiple steps, in one case the steps are 6 dB each. When the power is turned on, the gain set to 0 dB.

So that the filter reacts correctly to the first byte sent, it is desirable that a Delete command is sent.

-8th-

- Q _

G.J.P.Barnes 18-4-1

If the input isolation amplifier 11 from the analog input signal overdrives, which in the present case at peak values of more than plus / minus 7 V occurs, a call for help (CSRQ equal to service request) is sent via the control module 3 submitted. This can be prevented by means of a solder bridge in the control module.

Such a filter has the following advantages:

1. It is easy to use because it is fully programmatic. With the current, manually adjustable Filtering it is time consuming to find a desired one Achieve spectrum with reasonable accuracy, because neighboring bands influence each other. With the filter according to the invention, the entire setting can be made with little effort by a computer take place.

2. It is versatile because by removing or adding filter modules up to 12 different octaves (i.e. 36 individual bandpass filters) can be selected and so the frequency range from 10 Hz to 40 kHz completely or can be partially covered.

3. Each filter module can be addressed in such a way that either three individual bandpasses are created or that Module acts as a bandpass filter (i.e. the three bandpass filters, each with a third octave, act together Octave filter).

4. In principle the same way, other filters and weighting networks are also possible. Such devices have already been built with weighting curves according to A, B and C standards and with psophometric weighting curves.

G.J.P.Barnes 18-4-1

3. An override detector immediately generates a corresponding message if the filter is overridden.

6. The filter has a large dynamic range, because on the one hand attenuated in the filter modules by up to 88 dB and on the other hand the input isolating amplifier can amplify up to 20 dB.

7. The fully modular slide-in design results easy handling of the device, as the modules can be easily repaired and replaced.

-AO-

- blank page -

Claims (2)

International Standard Electric Corporation, New York G.J.P.Barnes - M.S.Hurley - A.R. Baxanda11 18-4-1 claims 1. Programmable filter with which an analog input signal attenuated in a desired manner as a function of frequency can be, characterized in that there are a number of filter modules (2) each containing a number of bandpasses (21) each with a third octave bandwidth, where an adjustable attenuator (22) for each bandpass filter (21) and an isolation amplifier (23) is associated therewith; that the outputs of the bandpass filters (21) have their assigned Isolation amplifier (23) are connected to an analog SignalaIsamme I line (45); that an input / output module (1) with
an input amplifier (11) is present, via which an analog signal coming from an analog input line (51) is sent to the bandpass filters (21) via the respective output weaker (22) is supplied; and that a control module
(3) is available, which via a connection bus (53)
Receives instructions and derives commands therefrom with which the bandpass filters (21) to be used are selected and the attenuation of the associated attenuator (22) is set will. ZT / P1-3S / BI May 10, 1984 -2- G.J.P.Barnes 18-4-1 2. Filter according to claim 1, characterized in that each filter module (2) three bandpass filters (21) each with one third Ls octave bandwidth and that these bandpass filters (21) are programmable so that they each contain a Octave filter result.